There are a number of factors influencing the development of economical and dependable state-of-the-art medical devices and surgical instruments, and the electromechanical systems, controls and sensors that may be incorporated into such devices. One factor is the healthcare cost savings that result from the use of reusable instruments instead of single use, disposable instruments or components which may be discarded as infectious waste. Another factor is the desirability of extending the ergonomic range provided by such devices to achieve a high degree of utility by both male and female surgeons. Yet another factor is the ever-increasing desire to demonstrate favorable patient outcomes while also demonstrating cost-effectiveness, especially in cases where access to cutting-edge surgical procedures and surgeons, real-time visualization of procedures, and precision have a clinical premium. Yet another factor is continued improvement in the automation and control provided by surgical instruments and empowering surgeons of a given skill level to consistently achieve excellent patient outcomes. Still another factor is the ever-increasing demand worldwide for affordable and modern healthcare solutions. All of these factors result in a desirability for reusable surgical instruments that continue to operate dependably after multiple exposure to cleaning, sterilization and operating environments.
Generally, it is desirable to decrease the environmental sensitivity of such surgical instruments and the electromechanical components, sensors, electronics and power sources upon which they rely. In order for an instrument to be reused following a given surgical procedure, it must be cleaned or washed, sterilized, and possibly recharged prior to reuse on another patient. Cleaning or washing may involve the removal of gross biological debris accumulated during a previous use. All blood, bodily fluids, tissue and any single use components may require removal or disassembly and cleaning with wipes, brushes, and/or enzyme-based detergents. Some single-use components, such as staple cartridges, may be utilized in reusable devices and require removal and disposal, as well as replenishment.
Cleaning and washing may involve exposing the surgical instrument to a special purpose washer, such as a dishwasher, which utilizes high temperature, high pH, aqueous detergents to automatically wash, neutralize and rinse the device. Neutralization may involve the use of a low pH solution (pH 2.6-3). After rinsing, the device is typically sterilized as a final step prior to surgical reuse. Sterilization is primarily achieved through steam in an autoclave. There are alternate methods for achieving sterilization as a final step, but steam sterilization is most common. Autoclaves are a preferred method of the medical industry for sterilizing surgical instruments and medical devices, including implants. Autoclaves involve variations of pressure and temperature in a sealed environment.
Surgical instruments may be exposed to other sterilization environments. For example, ETO (ethylene oxide), peroxide and wet-sterilization soaks, such as those sold under the name CIDEX®, may be utilized. Radiation may also be used in such procedures. Thus, reusable surgical instruments must be robust and resistant to degradation and contamination that may result from repeated exposure to such environments.
Medical devices and surgical instruments often incorporate electric motors for providing electromotive power to such devices. For example, a shaver designed for arthroscopic applications may employ a miniature electric motor for driving a shaving blade to precisely remove soft tissue in an arthroscopic surgical procedure. Such instruments, and therefore the motors that power them, may be exposed harsh environments in washing and sterilization processes as well as in the devices surgical operating environment itself.
The operating environment for a surgical device may present additional environmental challenges. For example, shavers that are used to trim and remove biological tissue may be operated in an arthroscopic surgical field, where the surgical field is viewed during the procedure with an endoscope, and a surgical space is created using pressurized surgical solution to which the instrument is exposed. The pressurized surgical solution may itself foster a harsh environment for the operation of the surgical instrument.
Operation of surgical instruments in environments that involve surgical solutions may add additional challenges that need to be addressed in the design of the instrument and in any electric motor or electromotive power component that may be integrated into the instrument. Such components may be exposed to a pressurized, aqueous and corrosive environment. Furthermore, the surgical solution may also be electrically conductive. Therefore, such components must be resistant to corrosion, resistant to ingress of pressurized fluid, and must electrically isolate the electronics and control components from the external environment. The high-iron alloys that may be typically used in magnetic circuits or other motor or control components may be particularly susceptible to corrosion, as are hardenable alloys, typically used in many long-life, rolling element bearing (REB) structures, such as 400 series allows. Still further, neodymium iron magnets that may be utilized in electric motors, may be susceptible to corrosion from surgical solutions. Such surgical solutions may also degrade the insulating properties of polymers used in surgical instruments as well as the lubricants and bearings used in motors and other components in the surgical instrument. The repeated use of reusable surgical components in surgical solution, cleaning and sterilization environments further compounds the detrimental effects of such environments on the integrity of a surgical device and electric motor components incorporated therein.
With particular regard to electric motors utilized in many surgical instruments, there are two areas where the harsh operating and sterilization environments may result in particularly detrimental effects on the motor components and thus motor operation and dependability. First, the motor may be more prone to bearing degradation or failure due to loss of lubricant (grease), corrosion and wear. Second, motor sensors, which may typically be Hall effect sensors in a brushless motor configuration, may be prone to degradation or failure due to moisture and ingress of surgical solution or other contaminants within the motor interior.
FIG. 1 illustrates a prior art electric motor configuration that may be used in a shaver surgical instrument, for example. The housing assembly 10 houses commutation magnets 12, front and rear ball bearings, 14 and 16, hall sensors 18 and stator 20. A printed circuit board (PCB) 21 may support electronic components, which among other functions, may provide control of current to the stator, based on information or analog signals from hall sensors 18. At least one stator to printed circuit board (PCB) lead connection 22 extends from the PCB to the stator. External leads 24 for power and control connections extend from the housing assembly 10. The PCB and hall sensors 18, as well as other components may be housed within a rear endbell 30. Such prior art configurations may be prone to ingress of surgical solution along the path “P” shown in FIG. 1, where deterioration of the seals may permit ingress from outside the housing assembly, across front bearing 14, along a space between the stator and rotor and to a space within the housing assembly where the stator to PCB lead connection 22 is exposed to the housing interior. Ingress of surgical solution or external contaminants may also occur along the space between the stator elements 20 and the housing wall, as well as through the endbell 30 and into an encapsulation compound used in sealing of the components within the rear endbell 30.
Thus, electric motor configurations of the prior art suffer from a number of disadvantages in being able to provide for continued reuse without contamination or other detrimental effects that result from exposure to harsh environments. It would therefore be desirable to provide electric motor structures for surgical instruments that address the aforementioned disadvantages and shortcomings and others.